The present invention relates to a cylinder lock device and, more particularly, to a cylinder lock with high resistance to destruction, and in which a rotated key cylinder is automatically returned to the original position by a spring.
In conventional cylinder locks, the proper key can be rotated to the locked position or the unlocked position in a key cylinder provided with tumblers that engage with a groove formed in a case. However, in such a conventional cylinder lock which prevents rotation of the key cylinder by means of the tumblers that are engaged with the groove of the case, there is a possibility that the cylinder lock is locked by destroying the tumblers. To solve this problem, as disclosed in, for instance, Japanese Unexamined Patent Publication No. Hei. 1-315569, a free-turn cylinder lock has been proposed in which a key cylinder is freely rotated when it is given rotational force in an illegal unlocking attempt. This type of cylinder lock has a sleeve rotatably incorporated in a case and the key cylinder rotatably supported in a second housing of a sleeve.
When the proper key is inserted into the key cylinder, the tumblers in the key cylinder are disengaged from the groove formed in the sleeve, to allow the key cylinder to be rotated relative to the sleeve. As a result, a slide ring engages with a lock-piece operating member and it becomes possible to actuate a lock device.
When an improper key is inserted into the key cylinder, the tumblers hold the key cylinder in the state of being engaged with the sleeve, to cause the key cylinder to be rotated together with the sleeve. Since the lock-piece operating member is not rotated, the lock device cannot be actuated.
When an improper key is used in the above type of free-turn cylinder lock, the key cylinder is allowed to freely rotate; that is, it is impossible to apply rotational force strong enough to destroy the tumblers. Thus, the cylinder lock can have high resistance to destruction.
On the other hand, in the free-turn cylinder lock, because of the structure in which the sleeve rotates together with the key cylinder when the key cylinder is rotated by an improper key, a return spring cannot be provided between the key cylinder and the case. Therefore, when rotational force is removed from the proper key after it is inserted into the key cylinder and rotated, the key cylinder does not automatically return to the original position. This requires cumbersome operations of manually returning the key to the original position and then pulling out the key from the key cylinder.